1. Field of the Invention
The present invention relates generally to heat exchanger construction and, more particularly, to the construction of a heat exchanger which eliminates the need for headers and thus is not only strong and lightweight but also achieves manufacturing efficiencies in its assembly.
2. Description of the Prior Art
Heat exchangers of various constructions are in widespread use, for example, in the automotive industry for use as automobile engine coolers, in climate control systems, as transmission and power steering oil coolers and the like. A typical heat exchanger construction for such applications comprises a pair of tanks, or headers, with finned tubes extending between the tanks. The tubes are usually formed flat so that fins may be attached to them as by brazing or other joining process. The flat tubes are inserted into slots formed in the tanks and are brazed in a furnace or welded in place. These tubes must fit tightly into the slots of the tanks or the joints formed therebetween may leak. An example of such construction is disclosed in U.S. Pat. No. 5,125,454 issued to Creamer et al.
The tanks themselves may be made from one-piece round pipe, or of sheet metal suitably stamped and formed. Generally, for round tanks, the maximum stress that the tank will perform under is represented by the expression Pd/2t, where d is the diameter of the tank, t is the thickness of the tank material and P is the maximum internal pressure of the tank. If the desired internal pressure of the tank if fixed, a heat exchanger with a large diameter tank can only withstand or operate at a lower pressure than a heat exchanger with a smaller diameter tank. Thus, in most cases the tank's material and diameter limit the heat exchanger's operating service pressure which in some applications requires the tank to be relatively heavy in construction.
Another disadvantage of heat exchangers which use header tanks is that the tank forming process typically involves stamping in the presence of an oil lubricant. Also, metal chips may be formed in the stamping process. As a result, the stamping requires a cleaning process to remove oil and metal chips from the tank after it has been formed. This increases costs of manufacture and as a result of the use of oils and cleaning solutions can also create environmental issues. Chips which are not removed from the tanks can contaminate the cooling system of the associated machinery and cause damage.
Accordingly, it is desirable to provide a heat exchanger which is constructed without the use of header tanks whereby oil and metal chip contaminants need not be removed in a separate cleaning process. It is further desirable to provide a heat exchanger which is capable of withstanding greater internal pressure, albeit with lightweight construction, by avoiding the use of header tanks. Still further it is desirable to provide a heat exchanger which avoids precise manufacturing processes as is necessary with known constructions using header tanks to ensure that the heat exchanger does not experience joint failure in use.